The New Zealand unit of World Wide Sires, the marketing arm of US-based Select Sires, says the Ministry for Primary Industries has confirmed there is no evidence imported bovine semen has developed a resistance to antibiotics used to treat cattle disease mycoplasma bovis.

In July, MPI said the disease had been detected in a dairy herd in South Canterbury, the first known outbreak in New Zealand.

Mycoplasma bovis is commonly found in cattle globally, including Australia.

It does not infect humans and presents no food safety risk, according to MPI.

The ministry took steps to contain the disease and is carrying out extensive testing to establish where the disease is present.

So far, it has only been detected on two of 16 farms belonging to the Van Leeuwen Dairy Group farms.

"New Zealand has been importing semen for many decades without incident and at this time there is no evidence that resistance has developed or that standard hygiene practices have been breached," according to an email from Angela Snell, a senior advisor on MPI's animal imports team, cited by World Wide Sires.

MPI officials were not immediately available for comment.

World Wide Sires New Zealand general manager Hank Lina said the company, along with other importers of bovine semen has been working with MPI to isolate and identify the source of the outbreak.

"We sell more than 19 million straws of semen to 80 countries around the world and, over several decades, have developed semen production and processing procedures which are amongst the most rigorous in the world," he said.

"Along with other semen companies, we were required to provide batch numbers and details of all bovine semen imported to New Zealand and potentially supplied to the Leeuwen group."